Definition of the applicability domain of the Short Time Exposure (STE) test for predicting the eye irritation of chemicals

Same-chemical comparison of nonanimal eye irritation test methods: Bovine corneal opacity and permeability, EpiOcular™, isolated chicken eye, ocular Irritection®, OptiSafe™, and short time exposure

The testing and classification of chemicals to determine adverse ocular effects are routinely conducted to ensure that materials are appropriately classified, labeled, and meet regulatory and safety guidelines. We have performed a same-chemical analysis using publicly available validation study results and compared the performance between tests for the same chemicals. To normalize for chemical selection, we matched chemicals tested by pairs of tests so that each matched set compared performance for the exact same chemicals. Same-chemical accuracy comparisons demonstrate a chemical selection effect that results in a wide range of overlapping false-positive (FP) rates and accuracies for all test methods. In addition, the analysis suggests that a tiered-testing strategy with specific combinations of tests can reduce the FP rate for some combinations. However, reductions in the FP rates were typically accompanied by an increase in the false-negative rates, resulting in minimal advantage in terms of accuracy. In addition, actual improvements in the FP rate after retesting positives with a second test are not as good as the theoretical improvements because some chemicals and functional groups appear to be broadly misclassified by all test methods, which, to the extent the tests make the same-chemical misclassifications, reduces the advantage of using tiered-testing strategies.

Expansion of the applicability domain for highly volatile substances on the Short Time Exposure test method and the predictive performance in assessing eye irritation potential

The Short Time Exposure (STE) test method is an in vitro method for assessing the eye irritation potential of chemicals and is used to classify the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) Category 1 and No Category (NC). The method has been adopted by the Organisation for Economic Co-operation and Development (OECD) as test guideline (TG) 491 since 2015. While this method can be used to classify GHS NC, it is not suitable for testing highly volatile substances and solids other than surfactants. Here we evaluated highly volatile substances to expand the applicability domain. According to TG 491, acetone, ethanol, iso-propanol, and methyl acetate as highly volatile substances resulted in false negatives. Saline was selected as a solvent of these false negatives. In this study, mineral oil was used as the solvent, because these false negatives were amphiphilic. Based on this change, four highly volatile substances were correctly evaluated. The predictive performance for classifying GHS NC was then verified using a substance dataset constructed in reference to the Draize eye test Reference Database and STE Summary Review Document. The accuracy and false-negative rate were 86.6% (194/224) and 3.8% (3/80), respectively. Collectively, the applicability domain was expanded by changing the solvent to mineral oil for highly volatile substances, and the predictive performance for the new applicability domain including highly volatile substances was excellent. The STE test method is suitable to classify GHS NC, indicating its applicability as a test method in a bottom-up approach.